The main aim is the evaluation and application of a model of optic nerve diseases which assumes that there are four major systems of axons in the optic nerve, which may be selectively damaged by certain diseases. The four proposed axon systems are B (blue sensitive), RGA (red-green color and acuity), F (flicker) and P (pupil light refles afferent). The model will be tested and a battery of psychophysical and physiological tests including spectral sensitivity curves, bichromatic mixture thresholds, color vision tests, contrast sensitivity functions, flicker modulation sensitivity and pupillometry. Optic nerve diseases to be studies include hereditary optic atrophies, toxic optic neuropathies, optic nerve compression, glaucoma and optic neuritis. The results will be correlated to the pathogenesis of the disease e.g. inflammation, pressure, vascular or toxic. These studies will involve the development and clinical evaluation of two visual testing systems controlled by microcomputers. Both systems can measure thresholds for a colored test spot as a function of visual field position and so may be used as perimeters or for measuring chromatic thresholds. The two systems are based respectively on a color television display and a maxwellian view optical system. An advantage of the color television system is that it can generate an equiluminous test stimulus i.e. a colored stimulus which has the same luminance as the surrounding screen and so can be detected only by a color-sensitive system. The maxwellian view system has the advantage of a greater range of intensities of test and background stimuli and the ability to measure spectral sensitivity curves.